This section provides background information related to the present disclosure which is not necessarily prior art.
As a result of environmental and other concerns, plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
Blow-molded plastic containers have become commonplace in packaging numerous commodities. Studies have indicated that the configuration and overall aesthetic appearance of a blow-molded plastic container can affect consumer purchasing decisions. For example, a dented, distorted or otherwise unaesthetically pleasing container may provide the reason for some consumers to purchase a different brand of product which is packaged in a more aesthetically pleasing fashion.
While a container in its as-designed configuration may provide an appealing appearance when it is initially removed from a blow-molding machine, many forces act subsequently on, and alter, the as-designed shape from the time it is blow-molded to the time it is placed on a store shelf in view of a consumer. Plastic containers are particularly susceptible to distortion since they are continually being re-designed in an effort to reduce the amount of plastic required to make the container. While this strategy realizes a savings with respect to material costs, the reduction in the amount of plastic can decrease container rigidity and structural integrity.
Manufacturers currently supply PET containers for various liquid commodities, such as juice and isotonic beverages. Suppliers often fill these liquid products into the containers while the liquid product is at an elevated temperature, typically between 155° F.-205° F. (68° C.-96° C.) and usually at approximately 185° F. (85° C.). When packaged in this manner, the hot temperature of the liquid commodity sterilizes the container at the time of filling. The bottling industry refers to this process as hot filling, and the containers designed to withstand the process as hot-fill or heat-set containers.
In many instances, container weight is correlated to the amount of the final vacuum present in the container after this fill, cap and cool down procedure, that is, the container is made relatively heavy to accommodate vacuum related forces. Similarly, reducing container weight, i.e., “lightweighting” the container, while providing a significant cost savings from a material standpoint, requires a reduction in the amount of the final vacuum.
External forces are applied to sealed containers as they are packed and shipped. Filled containers are packed in bulk in cardboard boxes, or plastic wrap, or both. A bottom row of packed, filled containers may support several upper tiers of filled containers, and potentially, several upper boxes of filled containers. Therefore, it is important that the container have a top loading capability which is sufficient to prevent distortion from the intended container shape.
More recently, container manufacturers have begun introducing multi-serve heat-set containers having a generally rectangular horizontal cross-sectional shape. Similar to the prior containers discussed above, these rectangular containers require a majority of the vacuum forces to be absorbed within the sidewall of the container. However, as these somewhat larger containers become increasingly lighter in weight, the weight of the fluid within the container reduces the amount of vacuum forces that the sidewall portion of the container can accommodate. Thus, this combination of lighter weight containers and increased weight of product within the container causes the sidewall portion of the container to sag and results in unwanted deformation in other areas of the container as well.
Moreover, as a result of the lighter weight containers, there has been an increased occurrence of deformation and/or damage of the containers during the filing and packaging process. That is, typically containers of this nature are processed along a series of stations, including for example a cooler station, combiner station, labeler station, case packing station, etc. The containers are transported along this series of stations via one or more conveyors upon which the container resides. The container typically engages the conveyor and is held in place simply by the frictional engagement of the bottom of the container (also known as the standing surface) and the conveyor belt. If any part of the series of stations needs to undergo reconfiguration, repair, and/or maintenance or is down for any reason, often times the remaining sections of the filling and packaging process continues, such that containers exiting one station are held before entering the next unavailable station. Therefore, a plurality of incoming containers on the conveyor will be pushed against other containers already in this staging area. The force of these incoming containers against existing containers (i.e. contact force) is dependent, at least in part, on the weight and rate of the incoming container along with the frictional contact of the incoming container with the conveyor.
Some attempts to minimize this contact force have included the use of lubricants disposed on the conveyor, near the staging area, to reduce the frictional connection between the incoming container and the conveyor. To this end, it is believed that the containers will more readily tolerate these contact forces and, therefore, be less likely to being damaged. However, due to the standing surface of most containers, these lubricants are often displaced and thus have short term benefits during system interruptions.